UWB wireless broadcasts are capable of carrying huge amounts of data up to 250 feet with extremely little transmit power and high immunity to interference and multipath fading. Indeed, the spread spectrum characteristics of UWB wireless systems, and the ability of the UWB wireless receivers to highly resolve the signal in multi-path fading channels due to the nature of the short duration transmitting impulse signals make the UWB systems a desirable wireless system of choice in a wide variety of high-rate, short- to medium-range communications. The ability to also locate objects to within one inch attracts the military, law-enforcement, and rescue agencies. Other applications include the broadband sensing using active sensor networks and collision-avoidance.
The circuit techniques that are used to realize different circuit components in a UWB transceiver are quite different from those proposed in current narrow bandwidth RF technology. Therefore, novel circuit topologies that achieve a gain-for-delay-tradeoff without affecting bandwidth, thus operating at substantially higher frequencies than conventional circuits, are desirable.
Generally, a few different methods have been used to achieve wideband characteristics of the RF front-end circuits, particularly with a low noise amplifier (LNA), which comes after the antenna and should be matched generally to 50 ohms (Ω), the impedance seen by the antenna. The first solution has been to use resistive feedback amplifiers (Kim et al., “An Ultra-Wideband CMOS Low Noise Amplifier for 3-5-GHz UWB System” IEEE Journal of Solid-State Circuits, Volume 40, Issue 2, February 2005 Page(s): 544-547). The disadvantage this type of wideband amplifier suffers is that at higher frequencies the input matching and gain drops due to parasitic capacitance. This type of wideband amplifier partially covers the UWB operational frequency band, more particularly, the lower band of UWB (e.g., 3-5 GHz). However, a bipolarversion of a resistive amplifier has been described that covers all of the UWB (Jongsoo et al., “A 3-10 GHz SiGe resistive feedback low noise amplifier for UWB applications”, Radio Frequency integrated Circuits (RFIC) Symposium, 12-14 Jun. 2005 Page(s): 545-548). DCR architectures for UWB have also been described to cover the lower frequency band UWB system (e.g., 3-5 GHz) (Razavi et al., “A. 0.13/spl mu/m CMOS UWB transceiver”, IEEE Solid-State Circuits Conference, 2005. 6-10 Feb. 2005 Page(s): 216-218; Iida et al., “A 3.1 to SGHz CMOS DSSS UWB transceiver for WPANs”, IEEE Solid-State Circuits Conference, 2005. 6-10 Feb., Page(s): 214-216).
The second solution has been to extend the narrow band technique to wide band using high order band-pass filtering to achieve the required wideband input matching (Ismail et al., “A 3-10-GHz low-noise amplifier with wideband LC-ladder matching network”, IEEE Journal of Solid-State Circuits, Volume 39, Issue 12, December 2004 Page(s): 2269-2277; Bevilacqua et al., “An ultrawideband CMOS low-noise amplifier for 3.1-10.6-GHz wireless receivers”; IEEE Journal of Solid-State Circuits, Volume 39, Issue 12, December 2004 Page(s): 2259-2268; Ismail et al., “A 3.1 to 8.2 GHz direct conversion receiver for MB-OFDM UWB communications”, IEEE Solid-State Circuits Conference, 2005. 6-10 Feb., Page(s): 208-210). However, this method suffers from sensitivity of the bandwidth to passive element variations due to processing. Moreover, the overall response of the wideband LNA is flat in the mid band, but generally rolls off at higher frequency due to the deviation from the 50 Ω reference impedance seen at the gate of the LNA input transistor. Also, the solutions described in the Ismail articles from 2004 and 2005 are designed using bipolar transistors.
The third solution has been to deploy a distributed architecture to achieve wideband characteristics on the front-end (Zhang et al., “Low power programmable-gain CMOS distributed LNA for ultra-wideband applications”, Symposium on VLSI Circuits, 2005. 16-18 Jun. 2005 Page(s): 78-81). The main advantage of a distributed architecture is its intrinsic wideband characteristics and, consequently, less sensitivity to component variations due to processing. In Zhang et al., a linear gain stage has been introduced as an LNA distributed along an artificial gate and drain transmission lines (T-lines), and it involves only linear operation of the distributed architecture.